A portable data carrier includes a radio frequency (RF) receiving circuit tuned to receive power signals on a carrier frequency, fc. The portable data carrier further includes a processor that uses a clock signal for operation thereof. A method of recovering the clock signal includes the steps of receiving timing information on a first sub-carrier frequency, fs1, that is offset from fc by a predetermined frequency. The timing information is then demodulated and the clock signal is extracted therefrom.
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10. In a portable data carrier comprising a processing element for processing a data signal, the processing element powered by a first power supply voltage and operable in response to a clock signal, a method comprising the steps of:
receiving a modulated signal; forming the first power supply voltage from energy in a carrier frequency of the inodulated signal; generating the clock signal in response to a sub-carrier frequency that is offset from a carrier frequency, fc, by a predetermined offset, fs1, of the modulated signal; and recovering the data signal by demodulating a portion of the modulated signal at the sub-carrier frequency down to baseband.
7. A portable data carrier, comprising:
a first receiving circuit tuned to receive power signals on a carrier frequency fc; a processing element, having a power supply voltage terminal operably coupled to the first receiving circuit for receiving the power signals thereon, that requires a clock signal for operation thereof; a second receiving circuit, operably coupled to the first receiving circuit and tuned to receive information signals on a first sub-carrier frequency that is offset from fc by a first predetermined frequency offset, fs1, the second receiving circuit providing both the clock signal and a plurality of data signals to the processing element.
1. In a portable data carrier that includes a radio frequency (RF) receiving circuit tuned to receive power signals on a carrier frequency, fc, the portable data carrier further including a processing element that requires a clock signal for operation thereof, a method comprising the steps of:
powering the processing element using the power signals; receiving an information signal on a first sub-carrier frequency that is offset from fc by a first predetermined frequency offset, fs1, wherein the information signal includes timing information; demodulating the timing information received, thereby producing demodulated timing information; and generating the clock signal from the demodulated timing information.
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The present invention relates generally to a portable data carrier designed for use in a contactless mode, and in particular to a method and apparatus for regulating power delivered to such a portable data carrier.
Portable data carriers (e.g., smart cards or chip cards are known to include a plastic substrate in which a semiconductor device (i.e., integrated circuit--IC) is disposed for retaining digital data. This digital data may constitute program instructions, user information, or any combination thereof. Moreover, these smart cards are known to be operational in a contacted mode, whereby an array of contact points disposed on the plastic substrate and interconnected with the semiconductor device is used to exchange electrical signals between the chip card an external card reader, or terminal. Similarly, there exists smart cards that operate in a contactless mode, whereby a radio frequency (RF) receiving circuit is employed to exchange data between the card and a card terminal. That is, the card need not come into physical contact with the card terminal in order to exchange data therewith, but rather must simply be placed within a predetermined range of the terminal.
Additionally, there exist smart cards that are alternatively operational in either a contacted mode or a contactless mode. Such cards are equipped with both RF receiving circuitry (for contactless operations) as well as an array of contact pads (for contacted operations). These smart cards are commonly referred to as combination cards, or combi-cards. It should be noted that in both the contact-only card and the combi-card arrangements, the array of contact pads typically conform to the ISO Standard 7816, which standard is incorporated herein by reference.
One of the problems of today's contactless smart card applications is the limited amount of information that can be modulated onto the carrier frequency. Indeed, some applications prohibit any modulation of the carrier frequency, thereby requiring another means for extracting transmitted information signals, other than the power signal transmitted on the carrier frequency, fc. Of course, there is a need for a transport of data signals as well as a clock signal that is to be used by the processing element of the smart card.
Prior art applications have tried to solve this problems using two-frequency systems, whereby the power signal was transmitted on a first frequency, and information (e.g. data signals and timing information) were transmitted on a second frequency. This implementation, which required additional circuitry on board the smart card where space is limited, resulted in a complex and costly solution. That is, because the discrete components required to receive RF signals from a terminal/reader, account for a great deal of the cost and complexity of a smart card system, adding another discrete receiving circuit to the card substantially increases the cost.
Accordingly, there exists a need for a method and apparatus for recovering a clock signal that is not constrained by the shortcomings of the prior art. In particular, a smart card apparatus that was able to reliably receive information without using the carrier frequency, and without adding substantial cost to the manufacture of the card, would be an improvement of the prior art.
The present invention encompasses a portable data carrier (e.g. a smart card) that includes a radio frequency (RF) receiving circuit that is tuned to receive power signals on a carrier frequency, fc. The smart card also includes a processing element requiring a clock-signal that is generated according to the present invention. An information signal is received on a first sub-carrier frequency varying in-frequency from fc by a predetermined amount fs1. The information signal includes timing information which is demodulated by the smart card and used to extract the clock signal for use by the processing element thereof. In this manner, the present invention solves the problems of the prior art by providing a cost effective technique for receiving the timing information from which a clock signal can be generated. Moreover, the carrier frequency need not be modulated to extract the clock signal.
The present invention can be better understood with reference to
As indicated, the sub-carrier frequencies are modulated using an amplitude modulation scheme. However, the skilled artisan will recognize that phase modulation is equally suitable for such an arrangement, and is simply a matter of design choice depending on system specifications. It is important to note that the sub-carrier frequency is not an integer harmonic of the carrier frequency, but rather comprises a pre-determined offset fs1 selected for optimum performance to reliably capture information signals. In one embodiment of the present invention, the sub-carrier frequency can be used both in the uplink (receiving) mode and the downlink (transmitting) mode. Again, this is a matter of design choice, and may be altered as later described.
Once the sub-carrier frequency is demodulated to extract the information signals, the processing element 103 proceeds to transfer data onto a multitude of buses and an internal registers bus (not shown) for use by the smart card 100. It is well known that such data transfers generate a convoluted noise signal, which is attributable to the data being switched and is commonly referred to as switching noise. The switching noise generated by the processing element 103 presents problems with the reception and transmission of information signals to and from the smart card 100. In accordance with a preferred embodiment of the invention, the sub-carrier frequency (or frequencies) can be advantageously selected to avoid the problems brought on by this switching noise signal, as next described.
In addition to selecting a first predetermined frequency offset, fs1, for the uplink transmission, a second predetermined frequency offset, fs2, can be chosen for the downlink transmissions. By way of example, frequencies 403 and 405 are selected to coincide in frequency with a second pair of quiet zones for the switching noise signal 401, as shown. As with the first sub-carrier frequency signal, the second sub-carrier frequency signal can be either phase modulated (as shown) or amplitude modulated, depending on the system requirements. (Note that the power response of the down-link sub-carrier frequency signals, 403, 405 appear to have a larger amplitude than their up-link counterparts. This is a result of the power spectrum curve being drawn from the perspective of the smart card, and is not a reflection of any significant power difference between the up-link and down-link transmissions.)
In a preferred embodiment, the second predetermined frequency offset, fs2, is selected to be an integer product of the first predetermined frequency offset, fs1. Of course, one skilled in the art will recognize that this is a result of the periodic nature of the switching noise signal 401. That is, once the switching noise signal is characterized as having a particular period, the first predetermined frequency offset is chosen to be one-half of that period (assuming it's maximum amplitude coincides with fc, as shown). Likewise, the second sub-carrier frequency is selected to be one or more full cycles away from the first sub-carrier frequency, as shown. In this manner, system performance (i.e., reception and transmission) can be optimized even in the presence of undesirable switching noise.
In the foregoing manner, the present invention provides a method for reliably recovering a clock signal even in the presence of unavoidable switching noise. Moreover, the carrier frequency need not be modulated to recover the clock signal or other data signals, as was done in prior art clock recovery schemes.
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